This invention relates to telephone systems and in particular, to resistance bridges used for interconnecting a plurality of subscribers' lines for conference purposes, data interchange, and the like.
A resistance bridge typically comprises a plurality of interconnected resistors and a plurality of terminal pairs for connection to subscribers' lines. The bridges may be two-wire or four-wire and may provide for handling various numbers of subscribers' lines, typically three-line or three-way to twentyfour-line or twentyfour-way. The specific embodiment described herein is for a two-wire system, but the invention is equally applicable to a fourwire system. A four way bridge is shown in FIG. 1. The apparatus shown in FIG. 2 includes four bridge boards, each of which can handle 24 two wire circuits thereby providing for 4 two wire six-way bridges, or 3 two wire eight-way bridges, or 2 two wire twelve-way bridges. The bridges can be constructed with different losses as desired by the telephone company.
Early embodiments of resistance bridges utilized separate resistors mounted on a circuit board, while more modern installations utilize printed circuitry. The resistive bridge is arranged to provide equal input and output impedances, usually 600 ohms, and large numbers of such impedance bridges are found in telephone equipment offices.
The resistance bridges are utilized for voice conferences and data interchange and typically operate at voice frequency (VF) in the range of 200 hertz to 23.5 kilohertz, as well as with a variety of communication lines including plain old telephone service (POTS).
From time to time problems arise in service utilizing resistance bridges and the telephone maintenance personnel must locate, identify and repair or replace the component or components causing the problem. Trouble shooting is accomplished by systematically disconnecting a subscribers line from a resistance bridge and substituting a terminating resistor for the subscriber's line. If the trouble is no longer present after this substitution has been made, the maintenance person knows that the problem is in the subscriber's line. Then the line can be tested and repaired. If the trouble is still present after a substitution, the substitution is reversed, that is, the terminating resistor is removed and the subscriber's line is reconnected, and the process is repeated for another subscriber's line. This is a difficult and time consuming approach which requires a maintenance person to work at the resistance bridge or at terminals leading to the bridge, which usually are found in crowded conditions of difficult access.
The problem of maintenance of resistance bridges is discussed in considerable detail in U.S. Pat. No. 4,338,496 which also presents a proposed solution. In the system of that patent, a two terminal jack is provided for each pair of bridge terminals and for each communication line pair, with appropriate interconnections between the jacks. The bridge and line interconnections are changed by manual insertion of appropriate plugs in the jacks. While the system of this patent does eliminate the necessity for unsoldering and resoldering of connections, it still requires the service personnel to be present at the bridge being tested and to manually effect the disconnection of communication lines and connection at terminating resistors.
It is an object of the present invention to provide a new and improved apparatus for use in testing resistance bridges. A particular object is to provide such apparatus which permits disconnecting and reconnecting of subscribers' lines and connecting and disconnecting of terminating resistors by service personnel at a location remote from the resistance bridge, and without requiring any physical movement of communication lines and/or terminating resistors. An additional object is to provide for such remote operation over existing equipment, such as a dual tone multi-frequency telephone hand set (DTMF) and a POTS lines.
It is an object of the invention to provide apparatus for testing resistance bridges which provides for disconnecting and reconnecting of individual lines very quickly and with a minimum of effort, thereby decreasing service requirement time and line down time. An additional object is to provide such apparatus which can be utilized with various types of communication lines, including VF and data, and two-wire and four-wire and various sizes of resistance bridges.
Other objects, advantages, features and results will more fully appear in the course of the following description, wherein the drawings merely show and the description merely describes the preferred embodiments of the present invention which are given by way of illustration of example.